Model-dependency The model-dependency of the Higgs width interpretation have been further discussed. The interpretation relies on the SM predicted ratio of off-shell/on-shell Higgs couplings, as the couplings run as a function of mass. This ratio would be distorted if a new light colored particle running in the ggH loop. (CMS paper, 1410.5440). In principle this could be eliminated by using VBF channel, which involves only HVV tree level coupling in both Higgs production and decay modes. Another possibility to invalidate the Higgs width interpretation is if additional light neutral Higgs bosons exist. (1412.7577) NLO status The NLO correction to gg->ZZ box diagram is not available at the moment. The bottleneck is the virtual correction with finite top mass in the loop. The current recipe is to apply same K factors of gg->H signal, with conservative uncertainties (further discussion needed?). In Sherpa+OpenLoops, NLO gg->ZZ is obtained by reweighting NLO gg->ZZ with infinite top mass, by the ratio of LO computation of the two scenarios (finite or infinite top mass). MCFM authors have computed the interference effects of ZZ+jet with H+jet (1409.1897). H+jet has large event rate, and slightly better signal background ratio than 0 jet category. Both gg and gq production modes are included. The effects are found qualitatively similar to the interference in the inclusive ZZ channel. This is a starting point to NLO computation when possible. Future potential Regarding what new constraints on Higgs properties by off-shell measurement are feasible in the future, it has been pointed out (1406. 6338, 1410.5806) the differential off-shell distribution provides a way to study top Yukawa coupling (kappa_t). If new particles are very heavy, the effects could be parameterized by higher dimensional operators. And the “far off-shell" tail is sensitive to these effects, i.e. could be used to disentangle kappa_t and kappa_g. At the HL-LHC, off-shell measurement could constrain kappa_t with ~25% precision with 3ab-1 data at 14 TeV. The analysis could be further optimized by, for example, application of Matrix-Element method. This is complementary to the top Yukawa precision measurement from ttH production, and the boosted Higgs study. -- Importance of off-shell measurement Complementary information w.r.t. on-shell measures Can be used to further constraint Higgs property (width / couplings) Indirect constraints -> theoretical assumptions when interpreting experimental results (example: SM-only states / specific EFT...) -- Example: Higgs width and the interpretation issue Underlying theoretical assumptions are clear Interpretation ambiguous if strong de-correlation of on/off-shell regimes Examples: strong modifications of the HZZ coupling, light d.o.f., new thresholds. Most of these effects cannot be studied within an EFT framework On one hand, it would be interesting to study concrete examples within benchmark models (first steps towards a classification e.g. in arXiv:1410.5440) On the other hand, interesting to investigate to which extent potential new physics effects which render the off-shell theoretical interpretation non-clean can be contstrained by complementary analysis, e.g.: - HZZ: lepton angular correlations, 4l invariant mass shape ( arXiv:1309.4819) - colored light d.o.f: Higgs pT ( arXiv:0809.1429) / boosted regime (arXiv:1410.5806) - new colored light d.o.f. would also affect the H->ZZ/H->gamma gamma mass-shift (along the lines of hep-ph/0302233) Information also from the VBF channel. Less statistics, but interpretation problems are milder (insensitive to light colored d.o.f. Still sensitive to light EW d.o.f.) -- Status of (SM) predictions Accurate predictions are needed for gg->(H)->4l process. Status: -Several parton-level MC publicly available (gg2VV, MCFM) -MCFM amplitudes implemented in the JHUGenerator for Higgs characterization studies (LO generator + Matrix Element method) -MCFM also studied H+J category So far, background amplitude only known at LO - Higher order estimated available, but for heavy top - bottleneck: complicated two-loop amplitudes. State of the art -> difficult to give time-frame estimates - first step: gg->VV through massless fermion loops - for a thorough analysis, also gg -> VV mediated by tops will be needed - for the signal: far off-shell one should start to worry about finite mT effects (afaik, no ones studied this issue yet). Sherpa+OpenLoops recently implemented correct LO reweighing for finite-mt effects (best we can do right now) -- Other topics covered in our task-force - H -> gamma gamma interference. Less model dependent, but very hard experimentally. VBF category can serve as control region. Feasibility studies for the HL-LHC - Hqq couplings -> could put some constraints at the HL-LHC. Will require however special trigger treatment, not very aggressive but should be planned well in advance -- In general Plenty of interesting physics, both from a SM and a BSM perspective. Relatively new field -> a lot of investigation needs to be done Cross-overs between SM production (precise predictions for bkg, finite mT effects...), EFT studies (coupling determinations...) and specific NP models (light d.o.f.). Tools: Run-1 MC - several parton-level LO tools for gg -> VV -> 4 leptons bkg. and interference available (studies for semileptonic VV decays in progress: gg2VV & MG5) - SM gg->VV (S/B/I): Sherpa+OpenLoops generates the gg->VV and gg->H(*)->VV processes with the merged 0+1 jet ME + PS. This is not the full NLO, but better than the LO in describing the hard real emission. (http://arxiv.org/abs/1309.0500) - VBF Madgraph and Phantom. The NLO corrections are less important here. Run-2 MC - NNLO qq->VV MC - gg->ZZ NLO calculations availability. - NLO for the VBF processes - gg->H+2j full calculation - Anomalous off-shell coupling MC. (More detailed info from Madgraph developers would be useful). - programs/studies for specific BSM models: real EW singlet model (Kauer-OBrien, Maina), MSSM (Englert-Soreq-Spannowsky) A theory related question is the limitations of the total width interoperation. There are quite a few comments or concerns regarding the total width interpretation (Engert&Spanowsky, Logan) - a thorough assessment of what value is added by off-shell/interference enabled Higgs analyses compared to on-shell Higgs analyses is desirable in the medium term - open questions for analysis techniques: where is matrix element method essential?, are used kinematic discriminants optimal?, other improvements? Priorities for YR4 need to be discussed/determined -------------------------------------------------------------- Off-shell Meetings: 1. HXSWG open meeting on off-shell and sig-bkg interference issues took place on 24th October 2014 with the following invited presentations: - Off-shell Higgs interference effects and width measurements in the ZZ decay channel, Raoul Rontsch (Fermilab) - EFT analysis of the off-shell Higgs data, Aleksandr Azatov (CERN) - MC tools: MadGraph5_aMC@NLO status report, Fabio Maltoni (Louvain) - MC tools: Sherpa+OpenLoops status report, Frank Krauss (IPPP Durham) - Interference effects in diphoton production for VBF, Nerina Fidanza (Buenos Aires) - Rare Higgs decays as probes for Higgs couplings to first- and second generation quarks, Stoyan Stoynev (Northwestern) 2. WG1 off-shell & WG2 Skype discussion on 13 January 2015 regarding kappa-framework extension to off-shell vs. EFT and BSM benchmark studies (to be continued at 22-24 January meeting at CERN and 3. meeting, see next) 3. WG1 off-shell & WG2 & WG3 virtual meeting to discuss model aspects of off-shell studies time: first week of February Doodle poll link: http://doodle.com/wdbuki378vi8fdfs